The voltage controller has a power input, an output, and a signal input. The power input is connected to a voltage source, and the voltage controller supplies at the output a constant voltage which is independent of voltage variations at the input.
European patent application No. 0 646 498 discloses an electrical system of this type. In this application, among others, a controller which includes a volatile memory is connected to the main and auxiliary lines. When the voltage on the main line drops, the voltage at the input of the controller, to which the main line leads, is buffered by means of an auxiliary source, i.e., a rechargeable battery. Further, the main line is connected to the auxiliary line by way of two serially connected decoupling diodes in-between which the auxiliary line is connected. Buffering the voltage on the auxiliary line is not disclosed.
Voltage controllers of this type are necessary to ensure a safe operation of electronic controlling and regulating devices in automotive vehicles. For example, a controller may be concerned which is used to control a hydraulic brake system by which the vehicle wheels shall be prevented from locking.
Typically, the power input of the voltage controller is coupled by a diode to the main line of the electrical system. The main line is directly connected to the battery (or by way of a safety fuse). This main line is usually referred to as `BAT`.
The input of the voltage controller is connected to the ground connection of the electrical system by way of a capacitor. The capacitor ensures that the power input of the voltage controller is fed with sufficient voltage even in the event of voltage breakdown on the main line, at least for a certain period (time of discharge of the capacitor).
Further, the voltage controller has a signal input which is connected to the auxiliary line of the electrical system. The auxiliary line is also connected to the positive pole of the battery by way of an ignition switch and is usually designated by the capital letters IGN (Ignition) in the automotive industry. When a voltage is applied to the signal input, an internal switch in the voltage controller is actuated, whereby the voltage controller is activated. The signal input is provided with a buffer capacitor, with the result that voltage breakdowns on the auxiliary line will not cause instantaneous deactivation of the voltage controller.
Shortcomings are involved with this external wiring of the voltage controller. Thus, two buffer capacitors are necessary, and the diodes connected upstream of the capacitors must be rated so that they can withstand the high charging current which occurs during activation.
Because increased temperature and voltage requirements are placed on both capacitors, it is not possible to increase the capacity of the capacitors as desired so that the length of the buffer time is limited. The result, in turn, is that voltage breakdowns of a long duration cause deactivation of the voltage controller.
In view of the above, an object of the present invention is to ensure by a simple external wiring of the voltage controller that in the event of voltage breakdowns, be it on the main line or the auxiliary line, the voltage controller remains active as long as possible so that the electronic components connected can be supplied with a constant voltage as long as possible.
This object is achieved by the present invention in that the auxiliary line is connected to the power input of the voltage controller additionally by way of a diode, and the diodes in the main line and in the auxiliary line are antiserially connected.
Consequently, this eliminates the need for the buffer capacitor that is normally provided on the main line because the buffer capacitor on the auxiliary line (adapted correspondingly), which is now the only one, may perform said purpose.